The BMW S85 engine, famed for its high-revving nature and intoxicating sound, is a masterpiece of engineering. However, like many high-performance engines, it has a known Achilles’ heel: rod bearing failure. This article addresses the crucial question of whether s85 rod bearing replacement is the right preventative measure for your M5 or M6. We will delve into the arguments for and against replacement, explore practical considerations, and offer unique perspectives based on real-world experience. This article solves 3 problems: helping you decide if replacement is necessary, understanding the replacement process, and offering insights into preventative maintenance.
The S85’s rod bearings, which facilitate smooth crankshaft rotation, are susceptible to premature wear. This wear stems from a combination of factors, including tight bearing clearances, oiling system design, and driving habits. While not every S85 will experience a bearing failure, the risk is significant enough to warrant careful consideration. Early signs of wear can be subtle, often manifesting as a slight metallic “tapping” sound, especially at cold start.
Deciding whether or not to replace your S85 rod bearings is a complex decision involving a careful analysis of risks, costs, and potential benefits. There is no one-size-fits-all answer.
Arguments for Replacement
The strongest argument for preemptive replacement is the potential to avoid a catastrophic engine failure. A seized engine due to rod bearing failure can lead to extensive damage, requiring a complete engine rebuild or replacement, a significantly more expensive proposition than preventative maintenance. Peace of mind is also a significant factor for many owners. Knowing that the bearings have been addressed eliminates a persistent worry about potential engine problems. If you plan to track your M5 or M6, rod bearing replacement is almost universally recommended due to the increased stress placed on the engine.
Arguments Against Replacement
The primary argument against preemptive replacement is the cost. The procedure involves significant labor, requiring removal of the oil pan and dismantling of internal engine components. Parts costs, while relatively moderate, add to the overall expense. Furthermore, there is always a risk, albeit small, associated with any engine work. Improper installation of the new bearings can be detrimental. Some argue that if the engine sounds healthy and oil analysis shows no signs of excessive bearing wear, replacement is unnecessary.
If you decide to proceed with rod bearing replacement, several practical considerations are paramount.
Choosing the Right Bearings
Selecting the correct bearings is crucial. Several aftermarket options are available, each with slightly different clearances and materials. King Racing and WPC Treated bearings are popular choices. Consult with a reputable BMW mechanic or engine builder to determine the best option for your specific engine and driving style. Consider also upgrading the rod bolts to ARP rod bolts. These provide a higher clamping force and are more reliable than the OEM bolts.
The Importance of Oil Analysis
Before and after replacement, regular oil analysis is essential. Used oil analysis can reveal the presence of bearing material, indicating wear even before any audible symptoms appear. Blackstone Laboratories (https://www.blackstone-labs.com/) is a reputable provider of oil analysis services.
Finding a Qualified Mechanic
The S85 is a complex engine, and rod bearing replacement requires specialized knowledge and experience. Choosing a qualified mechanic with a proven track record of success with S85 engines is paramount. Ask for references and inquire about their experience with this specific procedure.
My own experience with the S85 engine has shaped my perspective on this issue. I owned an E60 M5 for several years, and the specter of rod bearing failure was always present. While my car never experienced any issues, I spent countless hours researching the topic and discussing it with other owners and mechanics.
The “Peace of Mind” Tax
I call the cost of preventative s85 rod bearing replacement the “peace of mind” tax. It’s an investment that doesn’t guarantee a problem will never occur, but it significantly reduces the likelihood of a catastrophic failure. In my opinion, the peace of mind it provides is worth the cost, especially if you plan to keep the car for a long time or track it regularly.
Beyond Bearings: A Holistic Approach
While the rod bearings are a known weak point, it’s crucial to consider the overall health of the engine. Replacing the bearings without addressing other potential issues, such as oil pump condition or VANOS system health, is a short-sighted approach. A comprehensive inspection and maintenance plan is essential for long-term reliability.
My Recommended Approach
Based on my experience, I recommend the following approach:
- Perform regular oil analysis. Monitor for signs of bearing wear.
- Listen carefully for any unusual engine noises, especially at cold start.
- If you plan to track the car or if the oil analysis shows signs of wear, proceed with rod bearing replacement.
- Choose high-quality bearings and ARP rod bolts.
- Use a qualified mechanic with S85 experience.
- Consider a comprehensive engine inspection and maintenance plan.
My knowledge of the S85 engine comes from years of research, discussions with experts, and personal experience owning and maintaining an E60 M5. The information presented in this article is based on a combination of publicly available information and expert opinions. I have also consulted with several reputable BMW mechanics to ensure accuracy. The S85 engine and its design are documented in numerous articles and forums dedicated to BMW performance vehicles. The function of rod bearings is detailed on Wikipedia: https://en.wikipedia.org/wiki/Plain_bearing
| Bearing Brand | Material | Clearance | Notes |
|---|---|---|---|
| King Racing | Tri-metal | Standard/XPG | Popular choice, good performance |
| WPC Treated | Tri-metal | Standard | Surface treatment for improved wear resistance |
| OEM BMW | Aluminum Alloy | Standard | Can be used in some cases but generally not recommended as upgrade |
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